Abstract: My long-term career goal is to contribute to cancer research as an independent investigator that will lead to better ways of treating cancer. It is well known that 90% of cancer patients die because of metastasis, which results in the spreading of tumor cells to different organs such as lung and bone. As an important step towards achieving my career goal, I joined the laboratory of Dr. Joan Massague, one of the leaders in breast cancer metastasis field for my postdoctoral training. Located in the world's premier cancer research institutes, Memorial Sloan Kettering Cancer Center, this research environment provides unparalleled resources and expertise from clinicians and basic researchers. Innovative research at MSKCC is encouraged and is complemented with inputs from the tri-institutional community comprising of Rockefeller University, Weill-Cornell Medical College and clinical input from investigators from the Memorial Hospital. My work in Dr. Massague's laboratory sheds light on how the tumor microenvironment responds to chemotherapy to benefit cancer cell survival. Our evidence from animal models and clinical samples suggest that chemotherapy induces a burst of cytokines including TNF- from several components of the tumor microenvironment such as endothelial and smooth muscle cells. An undesirable consequence of the stromal TNF- is to boost CXCL1/2 expression in breast cancer cells. A higher level of CXCL1/2 then drives the paracrine loop involving myeloid cell-derived S100A8/9 to enhance cancer cell survival. An adverse cycle involving TNF--CXCL1/2- S100A8/9 could thus be expanded in response to chemotherapy. Once initiated, this chemo- protective program could become self-sustaining, leading to the enrichment of residual aggressive clones able to resist chemotherapy and thrive in the lung parenchyma and elsewhere. Obtaining a transitional award would be an ideal stepping-stone to independence with a mentored and independent phase. Based on our previous findings, my research plan critically addresses the role of the TNF--CXCL1/2-S100A8/9 axis in chemoresistance and metastasis in two different cancer types, breast and lung cancer. In the case of breast cancer proposed for the K99 phase, based on our work I will interrogate the link between chemotherapy, kinetics and biology of myeloid cell recruitment and metastasis progression in breast cancer models. The second aim will focus on devising ways of targeting the TNF--CXCL1/2-S100A8/9 axis most effectively. During this time, I will gain training in the area of lung cancer and familiarize myself with lung cancer metastasis models. In my independent phase, I will continue to focus on the components of the TNF--CXCL1/2-S100A8/9 axis (GOIs) that are activated with chemotherapy or during metastasis. In Aim 4, I will dissect the functional contribution of the GOIs in mediating chemoresistance linked metastasis.